Merge branch 'dev'
Merge branch 'dev'

Porting to Bootstrap 3 completed.
Merge branch 'dev'
Merge branch 'dev'
Merge branch 'dev'
Correct $extraClass behavior

The extraClass, if defined, must not prevent col-sm-5 on a form field.
Update colorbox to 1.4.37

This solves the scrollbar problem raised by the silverstrap 2 update.
Improve external reference handling

Moved all external dependencies on its own template
(templates/Includes/Silverstrap.ss) to have cleaner code.
Inline javascript for autotoc handling has been put inside
js/silverstrap.js.
Remove .ss-buttons, no more required by silverstripe-project